The present invention relates generally to plasma arc torches and more particularly to devices and methods for generating and stabilizing a plasma stream.
Plasma arc torches, also known as electric arc torches, are commonly used for cutting, marking, gouging, and welding metal workpieces by directing a high energy plasma stream consisting of ionized gas particles toward the workpiece. In a typical plasma arc torch, the gas to be ionized is supplied to a distal end of the torch and flows past an electrode before exiting through an orifice in a tip, or nozzle, of the plasma arc torch. The electrode (which is one among several consumable parts in a plasma arc torch), has a relatively negative potential and operates as a cathode. Conversely, the torch tip constitutes a relatively positive potential and operates as an anode. Further, the electrode is in a spaced relationship with the tip, thereby creating a gap, at the distal end of the torch. In operation, a pilot arc is created in the gap between the electrode and the tip, which heats and subsequently ionizes the gas. Further, the ionized gas is blown out of the torch and appears as a plasma stream that extends distally off the tip. As the distal end of the torch is moved to a position close to the workpiece, the arc jumps or transfers from the torch tip to the workpiece because the impedance of the workpiece to ground is lower than the impedance of the torch tip to ground. Accordingly, the workpiece serves as the anode, and the plasma arc torch is operated in a xe2x80x9ctransferred arcxe2x80x9d mode.
One of two methods is typically used for initiating the pilot arc between the electrode and the tip. In the first method, commonly referred to as a xe2x80x9chigh frequencyxe2x80x9d or xe2x80x9chigh voltagexe2x80x9d start, a high potential is applied across the electrode and the tip sufficient to create an arc in the gap between the electrode and the tip. Accordingly, the first method is also referred to as a xe2x80x9cnon-contactxe2x80x9d start, since the electrode and the tip do not make physical contact to generate the pilot arc. In the second method, commonly referred to as a xe2x80x9ccontact start,xe2x80x9d the electrode and the tip are brought into contact and are gradually separated, thereby drawing an arc between the electrode and the tip. The contact start method thus allows an arc to be initiated at much lower potentials since the distance between the electrode and the tip is much smaller.
With either start method, distribution and regulation of the plasma gas utilized for forming the plasma stream is typically provided by a separate element commonly referred to as a gas distributor or a swirl ring. Additionally, a secondary gas for stabilizing the plasma stream is often provided through another separate element or a combination of elements within the plasma arc torch such as passageways through a shield cup or between a shield cup and another consumable component such as a tip. By way of example, a gas distributor such as that described in U.S. Pat. No. 6,163,008, which is hereby incorporated by reference, is primarily responsible for regulating the plasma gas in a gas passage leading to a central exit orifice of the tip. The secondary gas is generally circulated through passages formed between a shield cup insert and the tip, and travels along the tip exterior to stabilize the plasma stream exiting the central exit orifice. Accordingly, several torch elements (i.e., gas distributor, shield cup, and tip) are required to distribute and regulate the plasma gas and the secondary gas.
Many of the consumable components, including the gas distributor, the tip, and the electrode, are often interchanged as a function of an operating current level in order to improve gas flow and form a stable plasma stream. For example, if a power supply is being used that operates at 40 amps, one set of consumable components are installed within the plasma arc torch to optimize cutting performance. On the other hand, if a power supply is being used that operates at 80 amps, another set of consumable components are typically installed to optimize cutting performance for the increased current level. Unfortunately, changing consumable components can be time consuming and cumbersome, and if an operator uses different operating current levels on a regular basis, an increased number of consumable components must be maintained in inventory to facilitate the different current levels.
Accordingly, a need remains in the art for a device and method to simplify operation of a plasma arc torch that operates at different current levels. Further, the device and method should simplify and reduce the amount of time required to change consumable components when operating at different current levels.
In one preferred form, the present invention provides a tip gas distributor that comprises a plurality of swirl holes and secondary gas holes, wherein the swirl holes direct a plasma gas to generate a plasma stream, and the secondary gas holes direct a secondary gas to stabilize the plasma stream. Accordingly, regulation of the plasma gas and secondary gas is controlled by a single torch component, which further provides a function as a tip, having positive, or anode, potential, in addition to metering the plasma stream during operation.
In another form, a tip gas distributor is provided that comprises a plurality of swirl holes, without any secondary gas holes, to direct a plasma gas to generate a plasma stream. Further, a tip gas distributor is provided that comprises a plurality of secondary gas holes, without any swirl holes, to stabilize the plasma stream. Additionally, tip gas distributors are provided that comprise at least one swirl hole and/or at least one secondary gas hole.
In other forms of the present invention, tip gas distributors are provided that comprise swirl passages and/or secondary gas passages formed between the tip gas distributor and an adjacent component rather than holes formed within the tip gas distributor. Similarly, the swirl passages direct a plasma gas to generate a plasma stream and the secondary gas passages direct a secondary gas to stabilize the plasma stream.
Additionally, methods of directing a plasma gas to generate a plasma stream and directing a secondary gas to stabilize the plasma stream are provided, wherein a source of gas is provided that is distributed through a plasma arc apparatus to generate a plasma gas and a secondary gas. The plasma gas is then directed through at least one swirl hole formed in a tip gas distributor of the plasma arc apparatus and the secondary gas is directed through at least one secondary gas hole formed in the tip gas distributor. Accordingly, the swirl hole directs the plasma gas to generate a plasma stream and the secondary gas hole directs the secondary gas to stabilize the plasma stream that exits the tip gas distributor. Moreover, methods of generating a plasma stream and stabilizing the plasma stream are provided that utilize at least one swirl passage and at least one secondary gas passage.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.